In the use of wrenches it is troublesome and time consuming to adjust the size of the jaw opening of the wrench to different sizes of bolt heads, nuts, or other objects to be engaged by the wrench. When work is done which requires frequent adjustment of the wrench jaw gap, much time may be wasted, and further, a bolt head or nut may be damaged by faulty wrench adjustment. This invention provides a wrench which is automatically adjustable to properly fit whatever is engaged by the wrench, within the limitations of the extent of adjustment of the wrench.